Pipeline natural gas is the primary fuel of choice for distributed fuel cell-based power generation systems because of its abundant supply and well-developed infrastructure. By using a fuel processing system at the unit inlet to reform the methane and higher hydrocarbons in natural gas, both solid oxide fuel cells and molten carbonate fuel cells will convert chemical energy directly into electrical energy for power distribution. Although processing of natural gas to remove sulfur is usually carried out close to the point of extraction, the processing leaves residual hydrogen sulfide as a contaminant at low concentration (e.g. 1-2 mg/m3). In addition to the naturally occurring hydrogen sulfide, pipeline natural gas usually contains other organic sulfur species that have been intentionally added as odorants.
The fuel reforming process requires heat, water vapor and a catalyst that enhances the chemical reaction rate. The most commonly used catalysts are nickel based. At the natural gas reforming temperature, the catalyst is highly susceptible to conversion into a metal sulfide if sulfur is present in the gas feed. This inactivates the catalyst and stops the reforming process. Therefore it is necessary to remove the sulfur from the gas flow to permit the desired fuel reforming to occur. In addition, sulfur that makes it through the reforming process will contribute to air pollution.
Advancement in the art of purifying materials has been made, such as with Kataoka, U.S. Pat. No. 6,828,141. However, this process is not regenerable, and does not have the specificity to sulfur as is needed. What is needed is a regenerable method and apparatus that can remove low levels of sulfur from a gaseous fuel flow.
Other difficulties with the prior art also exist, some of which will be apparent upon further reading.